1. Field of the Invention
The present invention relates to a manufacturing method for an orifice plate which forms an ink discharging portion of an ink jet printer.
2. Description of the Related Art
As a manufacturing method for an orifice plate which forms an ink discharging portion of an ink jet printer, the following method is conventionally known. In such a conventional manufacturing method, a photoresist having a nonconductive characteristic is first provided on a substrate having a conductive characteristic in accordance with a predetermined pattern, thereby preparing a master. An electroformed film made of nickel, which will later become an orifice plate, is then formed on the master by a known electroforming method. Finally, the electroformed film is separated from the master to thereby obtain the orifice plate.
An example of the conventional manufacturing method for the orifice plate will now be described with reference to FIGS. 5A to 5D. FIGS. 5A to 5D illustrate the exemplary conventional manufacturing method for the orifice plate in chronological order.
First, a photoresist 2 of a positive type is uniformly applied onto a conductive substrate 1 by a known spin coating method. As an example of the positive type photoresist 2, naphtho-quinone-diazide is known. The naphtho-quinone-diazide has an alkali insoluble characteristic. After dropping 2-3 cc of the naphtho-quinone-diazide on the conductive substrate 1, the conductive substrate 1 is retained by a spin coater and is rotated at 5000 rpm for 20 seconds. As a result, the photoresist 2 is uniformly coated on the conductive substrate 1. Thereafter, the conductive substrate 1 on which the photoresist 2 is coated is prebaked in a clean oven at about 90.degree. C. for about 30 minutes. As a result, the positive type photoresist 2 having a thickness of about 1 .mu.m (micro-meter) is formed on the conductive substrate 1. Thereafter, a photomask 3 having a light shielding portion 3A with a predetermined pattern is placed on an upper surface of the photoresist 2. The photomask 3 is a thin sheet or a thin plate having a characteristic of transmitting at least an ultraviolet light, so that light is permitted to penetrate only a light transmitting portion of the photomask 3, not the light shielding portion 3A. The light shielding portion 3A is constituted of a plurality of circles each having a diameter of about 152 .mu.m. The light shielding portion 3A is made of chromium (Cr), for example, and the circles constituting the light shielding portion 3A are formed on the photomask 3 at predetermined intervals, e.g., at intervals of 680 .mu.m. An ultraviolet light 4 radiates the photomask 3 from the upper side thereof, so that the photoresist 2 is exposed to the ultraviolet light 4 through the light transmitting portion of the photomask 3. The photoresist 2 exposed to the ultraviolet light 4 becomes ketene, and the ketene reacts with water in the air to become indene carboxylic acid. The indene carboxylic acid has an alkali soluble characteristic. On the other hand, a portion of the photoresist 2 located just below the light shielding portion 3A of the photomask 3 is not exposed to the ultraviolet light 4. Thus, this portion of the photoresist 2 remains naphtho-quinone-diazide (FIG. 5A).
Secondly, the conductive substrate 1 from which the photomask 3 has been removed is dipped into a developer liquid such as an alkaline solution, e.g., an aqueous solution of sodium hydroxide (NaOH). That is, as the photoresist 2 exposed to the ultraviolet light 4 in the above step has become indene carboxylic acid which has an alkali soluble characteristic, the photoresist 2 is dissolved in the aqueous solution of sodium hydroxide. As a result, a plurality of columnar photoresist portions each having a diameter of 152 .mu.m and a height of 1 .mu.m are formed on the conductive substrate 1 at intervals of 680 .mu.m. Thereafter, in order to remove moisture from the conductive substrate 1, the substrate 1 is placed in a clean oven and is baked in the clean oven at about 130.degree. C. for about 30 minutes, thereby improving an adhesion strength between the columnar photoresist portions and the conductive substrate 1 to some extent and solidifying the photoresist portions themselves. Accordingly, the columnar photoresist portions formed on the conductive substrate 1 are more stabilized and secured. In this manner, only the portion of the photoresist 2 not exposed to the ultraviolet light 4 is left on the conductive substrate 1 as a photoresist pattern 2A corresponding to the pattern of the light shielding portion 3A of the photomask 3. Thus, the photoresist pattern 2A is formed on the conductive substrate 1 to prepare a master (FIG. 5B).
A releasing film 5 is then formed on the master. The releasing film 5 is a high-molecular film mainly composed of a thiazole compound (the tradename, NIKKANON TACK manufactured by NIHON KAGAKU SANGYO CO., LTD.). Thereafter, an electroformed film 6 is electrodeposited by a necessary amount on the releasing film 5 by an electroforming method. The electroforming method is carried out in the following manner, for example. First, a nickel electrode and the master with the releasing film 5 thereon are dipped into an electroforming liquid such as nickel sulfamate. A current is then applied between the nickel electrode as an anode and the master as a cathode. As a result, the electroformed film 6 of nickel is electrodeposited on the master. At this time, a thickness and quantity of the electroformed film 6 may be changed by changing a current duty period or a total current quantity (FIG. 5C).
Finally, the electroformed film 6 is separated from the conductive substrate 1, thereby resulting in a manufactured orifice plate 7 (FIG. 5D).
However, in the conventional manufacturing method for the orifice plate as described above, the adhesion strength between the photoresist pattern 2A and the substrate 1 is not very large, and furthermore, the photoresist pattern 2A itself is not very hard. For these reasons, the following problems occur. That is, in releasing the electroformed film 6 from the conductive substrate 1 in the last step, there is a possibility that the photoresist pattern 2A partially sticks to the electroformed film 6 and is separated together with the electroformed film 6 from the conductive substrate 1. Accordingly, the photoresist pattern 2A on the conductive substrate 1 is damaged. The conductive substrate 1 with the damaged photoresist pattern 2A cannot be reused as the master for the manufacturing of the orifice plate. If the conductive substrate 1 with the damaged photoresist pattern 2A is intended to be reused, the whole of the photoresist pattern 2A must be removed from the conductive substrate 1 and a new master must be prepared by performing the above steps again, which results in an increase in manufacturing cost.
Even if the above problem does not occur, another problem occurs as will be described below. That is, in the course of repeated manufacturing of the orifice plate with the use of the master, the conductive substrate 1 itself is contaminated. Accordingly, the contaminated conductive substrate 1 must be washed. In washing the conductive substrate 1, an organic solvent such as an alkaline aqueous solution having a strong detergent is preferably used. However, since the photoresist pattern 2A is soluble in the alkaline aqueous solution, the alkaline aqueous solution cannot be used for the washing of the conductive substrate 1. Accordingly, the contamination of the conductive substrate 1 cannot be sufficiently eliminated, so that a quality of the orifice plate to be manufactured by repeatedly using the same master is reduced. As a result, the number of times of usage of the master is limited, causing an increase in manufacturing cost of the orifice plate.